Diclofenac sodium is sold as non-steroidal anti-inflamatoric antipyretic analgesics in the form of tablets, capsules or suppositories for the purpose of systemic action. When diclofenac sodium is orally administered, side effects on the stomach, such as stomach unpleasant feelings, occur. To reduce such side effects, therefore, preparations for transdermal absorption of diclofenac sodium have been studied.
Because diclofenac sodium hardly dissolves in water and an oil base, external preparations containing diclofenac sodium are prepared in the state of dispersion of diclofenac sodium. However, transdermal absorption of diclofenac sodium is not good in the state of dispersion preparations. Accordingly, techniques to dissolve diclofenac sodium in external preparations by additives have been developed.
There are, for instance, known external preparations, such as oil ointments characterized in using propylene glycol etc. as a solubilizing agent in order to solve the problem on insolubility of diclofenac sodium in an oil base (Japanese Patent Publication No. 59-33211), gel preparations characterized in using a definite amount of an alcohol, considering that diclofenac sodium dissolves well in an alcohol (Japanese Patent Publication No. 59-76013), emulsion preparations characterized in using a fatty acid and a carboxylic acid dialkyl ester (Japanese Patent Publication No. 64-13020).
Furthermore, following preparations are proposed: poultices characterized in using ethanol/water as a solvent, poultices characterized in using an alkylene glycol having 3 to 4 carbon atoms as a solvent with maintaining moisture (Japanese Patent Publication No. 61-60608), patches containing styrene-isoprene-styrene block copolymer and crotamiton (Japanese Patent Publication No. 4-321624), preparations for transdermal administration characterized in using a base consisting of a fatty acid ester, an alcohol and water (Japanese Patent Publication No. 6-321771), transdermal preparations containing urea or sodium edetate (Japanese Patent Publication No. 6-48939) and so on.